Tire with tread for combination of low temperature performance and for wet traction

Abstract

This invention relates to a tire with tread for promoting a combination of wet traction and service at low temperatures of a rubber composition containing a styrene/butadiene elastomer, cis 1,4-polybutadiene rubber, liquid high Tg styrene/butadiene polymer, resin and vegetable triglyceride oil.

Claims

1. A pneumatic tire having a circumferential rubber tread of a rubber composition comprised of, based on parts by weight per 100 parts by weight elastomer (phr): (A) 100 phr of styrene/butadiene elastomer and cis 1,4-polybutadiene rubber together with liquid styrene/butadiene polymer comprised of; (1) about 25 to about 75 phr of a styrene/butadiene elastomer having a Tg in a range of from about 35 C. to about 5 C. and an uncured Mooney viscosity (ML1+4) 100 C. in a range of from about 60 to about 100, and (2) about 25 to about 75 phr of high cis 1,4-polybutadiene rubber having a Tg in a range of from about 100 C. to about 109 C., a cis 1,4-isomeric content of at least about 95 percent and an uncured Mooney viscosity (ML1+4) 100 C. in a range of from about 50 to 100, together with (3) about 3 to about 50 phr of low molecular weight liquid styrene/butadiene polymer having a number average molecular weight in a range of from about 3,000 to about 30,000 and a Tg in a range of from about 30 C. to about 0 C., (B) about 50 to about 250 phr of rubber reinforcing filler comprised of a combination of precipitated silica and rubber reinforcing carbon black in a ratio of precipitated silica to rubber reinforcing carbon black of at least 9/1, together with silica coupling agent having a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with said diene-based elastomers and polymer, (C) about 5 to about 35 phr of traction promoting resin consisting of styrene-alphamethylstyrene resin having a softening point in a range of from about 60 C. to about 125 C. and a styrene content of from about 10 to about 30 percent, and (D) about 10 to about 50 phr of vegetable triglyceride oil comprised of soybean oil wherein said styrene/butadiene elastomer is a functionalized tin or silicon coupled elastomer having functional groups comprised of at least one of amine, siloxy and thiol groups reactive with hydroxyl groups on said precipitated silica.

2. The tire of claim 1 wherein said tire is sulfur cured.

3. The tire of claim 1 wherein said tread rubber composition further contains up to 25 phr of at least one additional diene based elastomer comprised of at least one of cis 1,4-polyisoprene isoprene/butadiene, styrene/isoprene, and 3,4-polyisoprene rubber.

4. The tire of claim 1 wherein said precipitated silica is a pre-formed composite of said precipitated silica and silica coupling agent.

Description

EXAMPLE I

(1) In this example, exemplary rubber compositions for a tire tread were prepared for evaluation for use to promote wet traction and cold weather (winter) performance.

(2) A Control rubber composition was prepared as Sample A with a precipitated silica reinforced rubber composition containing styrene/butadiene rubber and cis 1,4-polybutadiene rubber together with a silica coupler for the precipitated silica reinforcement.

(3) Experimental rubber compositions were prepared as Samples B through D with one or more of soybean oil, liquid styrene/butadiene polymer, liquid polyisoprene polymer and styrene-alphamethylstyrene resin being added to the rubber composition containing elastomers as styrene/butadiene rubber and cis 1,4-polybutadiene rubber.

(4) The rubber compositions are illustrated in the following Table 1.

(5) TABLE-US-00002 TABLE 1 Parts by Weight (phr) Control Exp'1 Exp'1 Exp'1 Material Sample A Sample B Sample C Sample D Styrene/butadiene rubber.sup.1 55 60 60 60 Cis 1,4-polybutadiene 45 40 40 40 rubber.sup.2 Rubber processing oil.sup.3 40 0 0 0 Soybean oil.sup.4 0 40 30 30 Liquid styrene/butadiene 0 0 0 10 polymer A.sup.5 Liquid cis 1,4-polyisoprene 0 0 10 0 rubber.sup.6 Styrene-alphamethyl- 10 20 20 20 styrene resin.sup.7 Precipitated silica.sup.8 125 125 125 125 Silica coupler.sup.9 7.5 7.5 7.5 7.5 Fatty acids.sup.10 5 5 5 5 Carbon black (carrier for 1 1 1 1 silica coupler) Wax 1.5 1.5 1.5 1.5 Antioxidants 3 3 3 3 Zinc oxide 2.5 2.5 2.5 2.5 Sulfur 1.2 1.5 1.5 1.5 Sulfur cure accelerators.sup.11 5 5.25 5.25 5.25 .sup.1A functionalized, tin coupled, styrene/butadiene rubber containing a combination of siloxy and thiol groups having a Tg of about 30 C. to 10 C. and Mooney viscosity (ML1 + 4) of about 70 as SLR4602 from Styron. .sup.2High cis 1,4-polybutadiene rubber as BUD4001 from The Goodyear Tire & Rubber Company having a Tg of about 102 C. .sup.3Rubber processing oil primarily comprised of naphthenic oil .sup.4Soybean oil as Sterling Oil from Stratus Food Company .sup.5Liquid, sulfur vulcanizable styrene/butadiene polymer having a Tg of about 22 C. .sup.6Liquid, sulfur vulcanizable polyisoprene polymer having a Tg of about 63 C. .sup.7Resin as styrene-alphamethylstyrene copolymer having a softening point in a range of about 80 C. to 90 C. (ASTM E28) and a styrene content in a range of from about 10 to about 30 percent as Resin 2336 from Eastman Chemical. .sup.8Precipitated silica as Zeosil 1165MP from Solvay .sup.9Silica coupler comprised of a bis(3-triethoxysilylpropyl) polysulfide containing an average in a range of from about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge as Si266 from Evonik. The coupler was a composite with carbon black as a carrier, although the coupler and carbon black are reported separately in the Table. .sup.10Fatty acids comprised of stearic, palmitic and oleac acids .sup.11Sulfur cure accelerators as sulfenamide primary accelerator and diphenylguanidine secondary accelerator

(6) The rubber Samples were prepared by identical mixing procedures, wherein the elastomers and liquid polymer with 80 phr of precipitated silica, together with silica coupler and compounding ingredients together in a first non-productive mixing stage (NP1) in an internal rubber mixer for about 4 minutes to a temperature of about 160 C. The resulting mixtures were was subsequently mixed in a second sequential non-productive mixing stage (NP2) in an internal rubber mixer to a temperature of about 160 C. with an additional 45 phr of precipitated silica. The rubber compositions were subsequently mixed in a productive mixing stage (P) in an internal rubber mixer with a sulfur cure package, namely sulfur and sulfur cure accelerator(s), for about 2 minutes to a temperature of about 115 C. The rubber compositions were each removed from its internal mixer after each mixing step and cooled to below 40 C. between each individual non-productive mixing stage and before the final productive mixing stage.

(7) The following Table 2 illustrates cure behavior and various physical properties of rubber compositions based upon the basic formulation of Table 1 and reported herein as Control rubber Sample A and Experimental rubber Samples B through D. Where cured rubber samples are reported, such as for the stress-strain, hot rebound and hardness values, the rubber samples were cured for about 14 minutes at a temperature of about 160 C.

(8) To establish the predictive wet traction, a tangent delta (tan delta) test was run at 0 C.

(9) To establish the predictive low temperature (winter snow) performance, the rubber's stiffness (storage modulus G) test was run at 20 C.

(10) TABLE-US-00003 TABLE 2 Parts by Weight (phr) Materials Control A Exp. B Exp. C Exp. D Styrene/butadiene rubber 55 60 60 60 Cis 1,4-polybutadiene rubber 45 40 40 40 Rubber processing oil 40 0 0 0 Soybean oil 0 40 30 30 Liquid styrene/butadiene polymer A 0 0 0 10 Liquid polyisoprene polymer 0 0 10 0 Resin 10 20 20 20 Properties Wet Traction Laboratory Prediction Tan delta, 0 C. (higher is better) 0.46 0.41 0.41 0.45 Cold Weather (Winter) Performance (Stiffness) Laboratory Prediction Storage modulus (G'), 3.4 3.1 2.8 2.7 (Pa 10.sup.6) at 20 C., 10 Hertz, 3% strain (lower stiffness values are better) Rolling Resistance (RR) Laboratory Prediction Rebound at 100 C. 48 46 48 49 Additional properties Tensile strength (MPa) 11.8 11.8 11.4 11.8 Elongation at break (%) 470 598 564 615 Modulus (ring) 300% (MPa) 6.7 4.9 5 4.8 Tear resistance.sup.1 (Newtons) 34 73 52 69 .sup.1Data obtained according to a tear strength (peal adhesion) test to determine interfacial adhesion between two samples of a rubber composition. In particular, such interfacial adhesion is determined by pulling one rubber composition away from the other at a right angle to the untorn test specimen with the two ends of the rubber compositions being pulled apart at a 180 angle to each other using an Instron instrument at 95 C. and reported as Newtons force (N).

(11) From Table 2 it is observed that:

(12) (1) For Experimental rubber Sample B, conventional petroleum based rubber processing oil of Control rubber Sample A was replaced with soybean oil, the SBR rubber was increased to 60 phr from the 50 phr of Control rubber Sample A, the resin increased to 20 phr from the 10 phr of Control rubber Sample A and the rubber Sample cured. As a result, an improved predictive cold weather (winter) performance was obtained based on a lower storage modulus G stiffness value of 3.1 as compared to a value of 3.4 for Control rubber Sample A. However, a loss in predictive wet traction was experienced based on a tangent delta value of 0.41 compared to 0.46 for Control rubber Sample A.

(13) (2) For Experimental rubber Sample C, the composition of Experimental rubber Sample B was changed by replacing 10 phr of the soybean oil with 10 phr of liquid polyisoprene polymer and the rubber Sample cured. A further improvement of predictive cold weather (winter) performance was observed as indicated by a beneficially even lower storage modulus G stiffness at 20 C. of 2.8 as compared to the value of 3.4 for Control rubber Sample A and value of 3.1 for Experimental rubber Sample B. However, similar to Experimental rubber Sample B, a loss in predictive wet traction was also experienced based on a tan delta value of 0.41 compared to 0.46 for Control rubber Sample A.

(14) (3) Experimental rubber Sample D was similar to Experimental rubber Sample C except that 10 phr of the soybean oil of Experimental rubber Sample B was replaced with a high Tg liquid styrene/butadiene polymer instead of the liquid polyisoprene polymer of Experimental rubber Sample C. An even further improvement of predictive cold weather (winter) performance was observed as observed by a beneficially even lower storage modulus G stiffness at 20 C. of 2.7 as compared to the value of 3.4 for Control rubber Sample A and 2.8 for Experimental rubber Sample C. However, an improvement in predictive wet traction was surprisingly discovered based on an observed tan delta value of 0.45 which compared favorably and beneficially to the value of 0.46 for Control rubber Sample A.

(15) It is thereby concluded from Experimental rubber Sample D of this evaluation that a unique discovery was obtained of a sulfur cured rubber composition composed of high Tg styrene/butadiene rubber and high cis 1,4-polybutadiene rubber (with its low Tg of about minus 102 C.) together with the combination of soybean oil, high Tg liquid styrene/butadiene polymer (Tg of 22 C.) and resin as shown in Experimental rubber Sample D, as compared to Control rubber Sample A. The desired target of improved cold weather (winter) performance (stiffness in a sense of storage modulus G at low temperature) without a loss of predicted wet traction (in a sense of higher tan delta values at 0 C.) for a tire tread performance was obtained from such a cured rubber composition.

(16) Further, a discovery is observed that Experimental rubber Sample D yielded a beneficially and significantly improved tear strength resistance value of 69 Newtons compared to a value of only 34 Newtons for Control rubber Sample A while maintaining a similar hot rebound value of 49 which is predictive of maintaining a beneficially similar rolling resistance for a tire tread of similar rubber composition.

EXAMPLE II

(17) Additional experiments were made with variations in liquid styrene/butadiene polymers (low viscosity SBR polymers).

(18) The rubber formulation recipes of Example I were used except for the liquid polymers being variations of the liquid SBR polymers.

(19) The experiments were composed of Control rubber Sample E with a formulation referenced in Example I, Table 1, as Control rubber Sample B, and Experimental rubber Samples F through H which contained additional liquid SBR polymers for comparison to the liquid SBR A evaluated in Example I. The liquid styrene/butadiene polymers used are reported in Table 1.

(20) The rubber Samples were prepared and tested in the manner of Example I. The following Table 3 illustrates cure behavior and various physical properties of rubber compositions.

(21) TABLE-US-00004 TABLE 3 Control Parts by Weight (phr) Materials E Exp. F Exp. G Exp. H Liquid SBR polymer A, 10 0 0 0 Tg = 22 C. Liquid SBR polymer B, 0 10 0 0 Tg = 14 C. Liquid SBR polymer C, 1 0 0 10 0 Tg = 6 C. Liquid SBR polymer D, 0 0 0 10 Tg = 61 C. SBR, solid, number average 4,500 8,500 10,000 8,600 molecular weight (Mn) Wet Traction, Laboratory Prediction Tan delta (higher is better) 0.52 0.53 0.55 0.49 Winter Performance (Stiffness) Laboratory Prediction Storage modulus (G') at 20 C. 10.8 12.4 11.9 12.1 (Pa 10 6) 10 Hertz, 3 % strain (lower stiffness values are better) Rolling Resistance (RR) Laboratory Prediction Rebound at 100 C. 51 49 50 48 Additional properties Tensile strength (MPa) 10.9 11 11.4 11.5 Elongation at break (%) 522 539 514 542 Modulus (ring) 300% (MPa) 5.2 5 5.6 5.3 Tear resistance (Newtons) 38 33 38 33

(22) From Table 3 it can be seen that all of the liquid SBR polymers with their varied range of Tgs provided the rubber compositions with similar low temperature predictive stiffness properties (G values) ranging from 10.8 to 12.4.

(23) However, Experimental rubber Sample H, which contained the liquid SBR with the lowest Tg of 61 C. (SBR polymer D), gave the worst predicted wet performance based on having the lowest tan delta value at 0 C. and therefore the liquid SBR polymer would be considered as having too low of a Tg for use in this rubber composition where a combination of wet traction and cold weather performance is desired.

(24) In contrast, Experimental rubber Sample G, having the highest Tg liquid SBR polymer gave the best predicted wet traction based on its tan delta value at 0 C., while sill giving similar predicted winter traction performance based on its G value at 20 C.

(25) Therefore it is concluded that to achieve a combination of high predicted wet traction together with beneficially low predicted stiffness (at low atmospheric temperature) for the tire tread rubber composition, a liquid (low viscosity) styrene/butadiene polymer with a high Tg would be desired to be combined with a high Tg, high molecular weight (evidenced by having a high uncured Mooney ML1+4 viscosity), styrene/butadiene rubber in the tread rubber composition which also contains the vegetable oil (soybean oil) to aid in reducing the overall Tg of the rubber composition to promote low stiffness for cold weather winter driving conditions, the cis 1,4-polybutadiene rubber having its low Tg of about 102 C. to aid in promoting low stiffness for cold winter driving conditions and traction resin to aid on promoting the tire tread's wet traction.

(26) It is concluded from these two laboratory studies that a liquid SBR polymer having a Tg in a range of about 30 C. to about 0 C. together with a number average molecular weight in a range of from about 3,000 to about 30,000 should be used for the rubber composition together with a solid SBR with a Tg in a range of from about 35 C. to about 5 C. and an uncured Mooney viscosity (ML1+4) in a range of from about 50 to about 150, alternatively from about 60 to about 100, to provide the beneficial combination of both improved low temperature stiffness (G) at 20 C. for cold weather winter performance and higher tan delta at 0 C. for wet traction for the silica-rich rubber composition comprised of a combination of high uncured Mooney viscosity (ML1+4) styrene/butadiene and cis 1,4-polybutadiene rubbers which contained both the aforesaid low molecular weight, high Tg, liquid SBR polymers and soybean oil and traction resin, when sulfur cured.

(27) While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.